Rubber products (such as tires, conveyor belts, vibration-insulating rubbers, and seismic isolation rubbers) are generally required to have high durability (such as fracture resistance, wear resistance, and crack growth resistance) and weather resistance. In order to meet such demand, various rubber components and rubber compositions have been developed. For example, WO2012/014455A (PTL 1) discloses a copolymer of a conjugated diene compound and a non-conjugated olefin in which the cis-1,4 bond content of the conjugated diene portion (units derived from a conjugated diene compound) is greater than 70.5 mol % and the non-conjugated olefin content is 10 mol % or more, and also discloses the use of the component for manufacturing rubber having good crack growth resistance and good weather resistance.
Such copolymer is a bipolymer obtained by polymerizing one kind of a conjugated diene compound and one kind of non-conjugated olefin, and a bipolymer thus obtained tends to be increased in crystallinity due to the increased content of the non-conjugated olefin units contributing to improving weather resistance. Such increase in crystallinity in copolymers involves a fear of damaging the physical properties as an elastomer, and also a fear of impairing workability in using such copolymers to produce rubber compositions and rubber products (in particular, in the process of kneading in producing rubber composition).